A well characterized system of host-parasite interactions is the Agrobacterium-higher plant system in which a soil pathogen induces hypertrophies on a wide variety of plants. The system is of considerable biological interest because it is the only one in which a piece of prokaryotic DNA is transferred, integrated and expressed in a eukaryotic cell. The broad outline of the molecular mechanisms by which Agrobacterium tumefaciens transfers a piece of T-DNA of its tumor-inducing (Ti) plasmid into plant cells has been elucidated. They involve the recognition of plant signals which induce the synthesis of enzymes concerned with the processing and transfer of T-DNA into the plant cell, and the subsequent expression of the T-DNA. Information on how integrated bacterial DNA (T-DNA) results in tumor formation is reasonably clear. However, the details of the early stages in plant cell transformation are poorly understood. This proposal is largely aimed at filling this gap in our understanding. Our studies are aimed at increasing our understanding of: (1) How Agrobacterium recognizes and uses specific plant signals to activate genes (vir) concerned with the processing and transfer of T-DNA into plant cells, (2) how DNA sequences in cis promote T- DNA processing, (3) what are the precise steps in the processing and transfer of T-DNA, and (4) what Ti-plasmid coded vir genes are involved. Are genes outside the vir region in any of these steps? These questions will be addressed through a combination of genetic and biochemcial techniques. These techniques include the isolation of novel regulatory mutants involved in vir gene expression, the continuation in sequencing of the vir operon, and overexpression of the vir genes. Antibodies will be made against all the vir gene products to help in their localization and purification. Selected gene products will be purified and characterized. These include the site specific endonuclease and any of the other Vir proteins whose purification would help in identifying its function. Studies on the Agrobacterium-plant system have revealed many similarities to bacterial pathogen- animal systems. Further, the Crown gall tumor aspects of this plant disease resemble viral induced tumors in animals in numerous respects.